Derives the F1-cov master field equation from substrate dynamics. Every mass has a finite gravitational domain R_d = (3M/8πρ_s)^(1/3). Sun: 363 light-years. Milky Way: 517 kpc. Validates against 175 SPARC galaxy rotation curves (χ²=1.31), KiDS-1000 weak lensing (χ²=0.007–0.067 versus NFW 5.77–6.57), and GW170817 carrier relaxation (τ_c predicted 4.6 ms; extracted ~6.8 ms). GR is recovered exactly in the quasi-static settled limit.